Started: Breeding Mice
Sounds Easy Doesn’t It?
Well, that’s not exactly true. Although mice have a reputation as
prolific breeders, there can be lots of complications, as with any animal.
Some mice may be infertile, which is more common than people think, or carry
lethal genes inevitably causing their offspring to die before or shortly
Selection of Parents
I think at one time or another we have all wished that we could choose
our parents… and breeding mice is a rare situation in that we can.
The mice we choose are very important for many reasons.
- Parenting Ability: Obviously it’s
very important that the babies will be looked after when they are born.
If you choose a skittish or nervous doe she might not do as well and
be reluctant to let you handle the litter. In the worst case she may
reject the babies due to lack of trust (if they smell of their human
owner too much too soon or have been frequently disturbed) and they
will either starve or the mother’s instinct will tell her to eat
- Hereditary Traits: If there are traits you
do not want to pass on e.g. whisker biting, barberism, or general unfriendliness
then this is the time to realise this and isolate those mice from your
breeding programme. If you are still keen despite some problems with
your desired mouse then you will have to weigh up the good and bad points.
Most of all you must be concerned with the well being of the animal.
However, some may not consider breeding certain mice because they intend
to show the offspring (see below).
- Colour Genetics: There have been volumes
written on this. It basically comes down to working out what colour
the offspring from a mating will be, using the parents’ genetic
make-up. For example, if you were breeding two self-blacks who both
had a gene for self-black colouring and a gene for self-lilac colouring
(taking SB as the dominant gene and SL as the recessive), your litter
is likely to be:
In other words, it is likely that one in four of the babies will be a
self-lilac. This sort of calculation can be used to ‘improve’
show stock lineage and eliminate undesirable features such as short tail
or small ears, as well as various markings and colourings.
- Illness/Health Problems: My housemate once
begged me repeatedly to breed her favourite of my mice, Niamh, because
she wanted to keep the litter. Despite her incessant pleading I had
to refuse because the mouse in question has a kinked tail. As many readers
will be aware, this could have led to painful spinal problems in her
young. Other problems that are important to avoid propagating are waltzing
and generally weak constitutions.
Have You Got the ‘Right Stuff’?
Once you have selected your best buck and doe (or trio; two does and a
buck) then you are a step closer. But first you have to make sure that
apart from a breeding pen you will also be able to house the babies for
at least five weeks before they go to new homes. They need to stay with
their mum all this time (although boys may be separated from the girls
and mum after four weeks). Breeders have to make sure that the mother
is not too bored but doesn’t have a cage filled with toys that will
cause her to become too active when pregnant, or cause a risk to the litter
when it is born. Personally, I would suggest a couple of wide cardboard
tubes and a cut up egg box (which she will also shred to make her nest)
make up her cage furniture. I take the wheel out in the last couple of
weeks of pregnancy until the babies are around three weeks old, just to
avoid any accidents.
So… Shall We Do It?
When you have met the criteria outlined for selecting your mice and think
you are ready to breed, there are a few rules you would do well to follow.
1. Make sure your breeding pen is big enough for the two mice to live
in for a week or so. They will not thank you if they are confined in a
tiny space, and will probably not get on as well either!
2. Clean out the tank thoroughly so it does not smell of a particular
mouse. Provide plenty of bedding, food and water.
3. You may want to introduce the doe and buck on your hands before putting
them in the tank together. If not, put the buck in first as does will
defend their territory against any invading bucks!
4. Make sure the tank is not in a draught or direct sunlight (as with
any tank). Try not to disturb them too much for the first few hours they
are together to allow them to adjust to their new situation. They will
probably sniff each other and the male may chase the female around but
this is normal. If the female is in heat she can become pregnant straight
When is the Best Time?
There are some things you should know when you intend to breed mice that
will make your life a lot easier and avoid unexpected litters. Does come
into heat on average every four or five days, during which time they can
get pregnant. They can also become pregnant again immediately after giving
birth on their postpartum oestrus (meaning they immediately come back
into heat), so if you do not want two litters back to back, which is inadvisable,
you must remove the male before the birth. However, if you do decide to
leave the male in with the female, he will make a good father and help
the mother to look after her babies. Having said this, you must take into
account that the female will be rearing two litters at the same time,
which will put extra strain on her body – especially in regard to
her milk-producing abilities.
When the mouse gives birth she will need no help from you and should be
left undisturbed. If she is in a quiet and darkish place she should be
just fine on her own. If she is living with other does they may help her,
acting as midwife and sharing the care of the litter. If anything goes
wrong and the mother abandons her babies they can be fostered to another
doe that has babies of the same age, who may adopt them and continue to
raise them. Otherwise, it is very hard to raise orphaned mice, as they
have to be fed at least every two hours to remain alive. However, it has
Most does give birth between 10pm and 2am, when mice tend to be the most
active. The babies announce their arrival (and so may mum) by squeaking
from within the nest. At this point they should not be disturbed, but
left alone for at least a day. It depends on the doe as to when you look
at the babies for the first time. If she trusts you, it may be possible
to look as early as day one, but if in doubt wait until day three. By
this time you really should check the nest if only to make sure that no
babies were stillborn.
When you want to look at the babies you must wait until the mother leaves
the nest voluntarily and remove her from the tank. This way she cannot
see you handling her babies and get distressed. A new mum often welcomes
the break and relishes the chance to run about in her ball after being
stuck in with her babies for three days! When mum is safely out of the
way, it is advisable to rub your hands in the dirty bedding to make them
smell more mousy and less human. Then you can gently lift up the bedding
and look at the babies, pick them up etc. Just remember that it is important
that they stay warm so do not keep them out of their nest for too long.
Your part may be relatively small but it is important. You must make sure
that mum has plenty of food and water. It is a good idea to give her fattier
food than usual while she is pregnant and lactating. Otherwise, keep handling
the babies and enjoy your litter!
Age at weaning: 3.5 weeks on average
Age at sexual maturity: 4-6 weeks
Recommended breeding age: Does – 3 months, Bucks –
10 weeks onwards
Gestation period: Average 19-21 days
Average time of birth: 10pm – 2am
Fur begins to grow: 7 days onwards
Eyes open: 13 days onwards
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